This invention relates to a weighing and packing device for making packages of product each containing a quantity of product having a weight equal or close to a predetermined value and, especially, to such device including a metal detector.
In a combination weighing machine as disclosed for example in U.S. Pat. No. 4,560,015, product is distributively fed to a plurality of weighers and the resultant weight values are combined in various fashion for selecting from the resultant combinations a combination having a total weight equal or close to a predetermined weight and discharging a batch of product forming the selected combination from the corresponding weighers at the same time. This operation is repeated for successively delivering batches of product of desired weight.
On the other hand, U.S. Pat. No, 4,288,965 discloses a form-fill-seal packing machine in which a web of flexible packing material is pulled from a supply roll and fed over a device for forming it into tubing, product to be packed is fed into the tubing and the tubing is sealed to form packages. When such a packing machine is coupled vertically with the above-mentioned combination weighing machine, a weighing and packing device is formed.
In a combination weighing and packing device, metal pieces might become mixed in with the product before it is fed to the weighers. For example, when the product is worked, broken pieces of a cutting tool may mix in or when the product is contained in a large bag before it is fed to the weighers, staples used for closing the bag may mix in with the product when the product is unloaded from of the bag. In the past, such product including any metallic substances has passed into the combination weighing machine and has been fed to the packing device and packed. This has created a problem in that the metallic substance may be swallowed by a consumer of this package.